This invention relates to a pulling tool, in particular for use in the positioning of equipment and acquisition of measured data in pipelines and boreholes for the production of oil and gas.
In long pipelines and boreholes there is often a need for putting down different equipment and collect measured data. For this purpose pulling tools of different embodiments are used, having wheels or chains that roll on the wall of the pipe or borehole. The rollers or the chain are/is pressed against the wall of the pipe/borehole with a force sufficient to achieve the desired axial propulsive force in varying frictional conditions. The supply of power is effected through a cable connection to the surface.
An optimum pulling tool must be formed to be able to negotiate restrictions and sharp curvatures without getting stuck. In order to achieve these important functions, a solution has been reached in the present invention, which makes it possible in a simple and robust way to meet these functional requirements. To achieve this object the pulling tool is provided with 3 axially longitudinal chains, offset 120 degrees relative to each other viewed in a section perpendicular to the longitudinal axis. The chains run on longitudinal links which are interlocked, so that the radial movement will be the same for all three chains when they are moved radially. With this construction is achieved that the pulling tool is always kept centred within a pipe or a borehole. This is a condition for allowing efficient positioning of equipment and operation of measuring tools.
A limitation in the length of the tool is achieved by all three links with chains being arranged in such a way that they have a radial movement out from the centre. In addition, the links are arranged 120 degrees offset relative to each other and with the same extent longitudinally. In most other known structures the pulling devices are arranged one behind the other, which makes the pulling tool long and unsuitable in sharp curvatures. In boreholes which have not been lined with steel pipes, the walls are often rough and it is difficult for wheels to achieve sufficient grip. In such events the use of chains would be advantageous.
Most known pulling tools utilize electric/hydraulic operation. This means that an electric motor drives a hydraulic pump, which again supplies power to hydraulic motors in the driving wheels. Such a system will be technically complex and low efficiency is achieved. With a limited supply of power through long cables, this will limit the traction substantially. In several operations great tractive power is desirable. In the present invention propulsion is effected through direct electric drive, without the use of hydraulics. Thereby a substantially higher performance is achieved for the pulling tool.